Our objective is to develop a new system for the study of synaptic structural plasticity in the mature brain. Using long term multi-photon imaging, we have found that synaptic connections in the adult Drosophila brain are dynamic, undergoing both formation and elimination over a period of several hours. This system offers to bring the power of Drosophila genetic analysis to bear on the question of synaptic structural plasticity within the CNS, and can be applied to regions of the brain with direct involvement in processes such as learning and memory. We seek support to develop this system into an important paradigm for the genetic analysis of synaptic plasticity. We will investigate the mechanism of this structural plasticity using multi- photon confocal imaging and image analysis methods. The structure of dynamic synapses will be investigated in detail by investigating their ultrastructure and function. A long-term imaging protocol for live behaving animals will be developed. Our initial studies indicate that hyper-activating neurons or over- expressing a gain-of-function Raf allele can induce changes in synapse architecture in the adult CNS. Whether neural activity regulates synaptic structural dynamics will be further addressed by imaging individual synapses while hyper-activating or suppressing activity in adult animals. To further explore the molecular mechanisms that regulate synaptic structure, we will initiate a large-scale genetic screen for regulators of synaptic architecture. Beyond the term of this proposal, these regulators will be characterized molecularly and studied in detail. Our ultimate goal is to manipulate the plasticity of the nervous system in order to provide avenues for restoring neural function after brain injury or disease. By understanding what molecules may regulate synaptic dynamics in a normal CNS, we may be able to induce specific changes in a brain damaged by disease or stroke, or that malfunctions in behavioral disorders. [unreadable] [unreadable]